This invention relates generally to electronic control circuits and deals more particularly with an improved vibratory amplitude controller for electromagnetically driven vibratory mechanisms such as vibratory feeders.
Vibratory feeders generally include bowls, bins, hoppers, or transport rails which are vibrated to cause or facilitate movement of a plurality of parts in a smooth, substantially uniform manner in a desired direction, and perhaps in a desired orientation. The movement of parts in such feeders is accomplished by oscillating a part supporting member, such as a bowl, in a path having vertical and horizontal components. In the case of a bowl feeder, the parts move up a spiraling inclined ramp, provided about the inner periphery of the bowl, from the bottom of the bowl to a discharge outlet generally located along the upper rim. Part orienting means may be utilized to align the parts in a desired manner to facilitate, for example, subsequent handling or packaging of the dispensed parts.
An electromagnetic drive unit may be provided to impart the vibratory motion to the bowl or other parts supporting member and it is often controlled in an attempt to cause the parts supporting member to vibrate at such an amplitude and frequency as to produce a desired parts feed rate. In connection with such control it is usually desirable to maintain a constant vibratory amplitude under varying load conditions such as those which occur as parts are dispensed from the feeder or when the bowl or other parts supporting member is refilled; that is, the vibratory amplitude should not increase or decrease as a result of changes in the vibrated mass, thereby maintaining the desired parts or product feed rate constant. Since the electromagnetic drive unit is generally operated from an electrical A.C. power source, variations in the A.C. input line voltage also may cause vibratory amplitude variations.
Vibratory apparatus control circuits, such as those illustrated and described in U.S. Pat. No. 3,122,690, assigned to the same assignee as the present invention, have been used to provide a means for automatically controlling vibratory amplitude variations under varying load conditions by controlling the amount of current supplied to the electromagnetic drive unit. Often these circuits are of the phase-shift control type having servo amplitude control using transducer means mechanically connected to the vibrating portion of the apparatus to sense the vibratory amplitude and provide a feedback signal to the control circuit tending to maintain a constant vibratory amplitude.
One drawback to the aforementioned vibratory amplitude control circuits of the prior art is the use of an external transducer connected to the vibratory apparatus for sensing the vibratory amplitude. Typically transducers, for example, ones using phototransistors or light emitting diodes, are fragile, adversely influenced by dirt and other environmental conditions and susceptible to breakage. Another drawback is the additional wiring required from the controller to such a transducer.
Some control systems are manually operable to adjust the vibratory amplitude to compensate for changes in container weight, A.C. input line voltage, temperature and conditions having an influence on the amplitude. But such manually controlled systems require constant operator attention to maintain a desired feed rate. Further, a tendancy of operators is to turn the amplitude control to full value regardless of the resulting apparatus performance or risk of damage to the product. Such operation creates a condition of potential overstressing of the vibratory apparatus component parts and increases power consumption which is energy, wasteful and inefficient.
One amplitude limiting arrangement aimed at overcoming some of the aforementioned problems, illustrated and described in U.S. Pat. No. 3,840,789, assigned to the same assignee as the present invention, uses a photoelectric transducer having a light source spaced from the light sensitive surface of a phototransistor and mounted on the fixed portion of the vibratory apparatus. A vane is mechanically connected to the movable portion and is positioned to interrupt the light beam to provide a feedback signal to limit the vibratory amplitude to a predetermined magnitude. Initial adjustment and alignment of the vane relative to the sensitive surface and subsequent replacement or servicing of the phototransistor and light source is difficult since the photoelectric transducer is often mounted in a relatively inaccessible location.
Accordingly, it is desirable to have a vibratory amplitude controller for use with vibratory mechanisms that maintains a constant vibratory amplitude under varying load and A.C. line input voltage conditions and that avoids the drawbacks of the aforedescribed controllers.
A general object of the present invention is to provide an improved vibratory amplitude controller for electromagnetic drive units used in vibratory feeders that overcomes the limitations of previously used vibratory amplitude control systems. The controller of the present invention is reliable, does not use additional external transducers, provides automatic drive compensation for changes in A.C. input line voltage, container weight and the like and is compatible with various vibratory feeder electromagnetic drive units.
Other objects and advantages of the invention will be apparent from the following written detailed description and from the accompanying drawings.